Regenerative heat exchanger



Jan. 5, 1954 U, o. BLoMQuls'r 2,665,120

REGENERATIVE HEAT EXCHANGER Filed Aug. 9, 1950 ATTORNEY Patented Jan. 5,1954 UNITE-D lSTIA"1"'ES PATENT REGENERATIVE HEAT .EXCHANGER 'Uno v010i":'Blomguist, Vasteras, Sweden 7 Claims.

This vinvention relates. to .rotary regenerative airpreheaters in `whicharotorenclosed in. ashell is .provided ywith .heat accumulatingvelements through which ue gasesand air pass `inanalterhating manner. Inair :preheaters of .this `type, there prevails a .considerable pressure.difference between the air duct-andthe-gas duct. Inorder to reduce thispressure difference, sealingA members have to be providedbetween the-rotor and the stationarypartsofthe preheater. .'Saidsealingmembers.usuallycomprisestrips arranged rae dially at the end facesof therotor and adapted to slide on sector ,plates .which separate the .airside from the gasside, the sealing ,members -further comprising stripsarranged circumferentially on the rotor andstrips disposed axiallybetween the rotor and the shell. 'In spite `of various vimprovements,particularly ,of the axially llocated sealing strips, for instance by.making them externally adjustable, it was not possible to reduce thelosses due to leakage to reasonable values. The major part ofthese'lossesjs `a result of .air leaking through the space between therotor and the shell from theair side to the,gas side of the preheater.On account ofthe 'leakage losses, the power required for the iluergasfan is considerably increased, and cleaning of' the flue gases 'in gaslters and ash separators is rendered more dilicult.

The invention vhas for its object' to "provide means for eliminating,entirely 'or'in part, "leakage from the air side to thegas'jside. Theinvention is characterized 'by a vdraught'fan connected to the spacebetween the rotor and theshell von the air side of the preheaterat alocation upstream from the air discharge port of .the shell forreducingthe pressure prevailing in `said space. The Adraught fan ispreferably devisedto reduce the pressure in said space down to thepressure which prevails on the .gas side in the spacebetween the rotorand the shell. Due to :this arrangement, leakage through said space isentirely eliminated. vSince the air .quantity which would leakthroughsaid space constitutes the major portion of air leaking betweentheair side and the gas side, theeinciencyof the preheaterisconsiderably increased due to the arrangementaccording tto theinvention. The .discharge -conduit of the fan is preferablyconnected tothe air duct in front of or lafter the preheaten In the last namedalternative, the discharge conduit of the fan may have inserted thereinaheat exchanger located in the gas duct. By means of this heatexchanger, the quantity of air Ipassing 'through the fan can tbelpreheated substantia11yfto-:the

-samei'temperature as .the main air stream.

The invention will now be described morezclearly with referenceito a thetwo. embodiments thereof .illustratedinmthe annexed drawing. i-'Figlshows lin .diagrammatic manneran elevation,'.'part1y in section, of4` apreheater embodying -this invention. FigZillustratesthe cooperationbetweenia sector Vplate vand -radial sealing strips; and .Figure `3 :iissimilarto Figure 1 but'zshowsa slightly modied embodiment of theinvention.

`The air preheater illustrated `comprisesiza..rotor 2 fadaptedltorotate;aboutsa .iveltticalfaxis l, said `rotor Vhaving .a--great numberof ,capa-ratively 'thinwalled plates .which may vbe corrugated :asvindicated in Fig. `2. The air :duct is =indicatediat3 :and thedirection of flow of air-through said 4ductis indicated by thefarrows'4. .The flue gases pass through the gasduct-S in .an oppositedirection, as indicated by thefarrows .6. The airduct and the gas ductlare separated from reach other by meansof. sector-shapedplates 1 and 8,on a'nhousing `,enclosing :the rotor, Vand in .contact with :radiallyextending sealing strips 9 fand i0, respectively, secured tothe rotor..-Itisto be understood,

of course, .thatthe vhousing .has axially aligned air .inletand outletIports with which the `inlet= and Outlet portionslof theair duct 3communicate; and gas inlet andoutletfports likewise communicatingwiththe gas inlet and outlet'portions of the fgasduct `ii. Therotor furtherhas vcircumferentiallyextending sealingstrips H andaxiallyextendingsealingstrips, not shown, between the periphery ,of .the-rotorand .-a shell 1.2.-whichsurrounds therotor andconstitutes part of therotor housing. Thatportion of the rotor .which during the .rotation ofthe rotor is. passed by :Huid gases, accumulates heatfrom the gasesandupon-.continued rotation transfers'heat to the air vpassing in acounteriiow direction through the -air duct. As willappear from Fig. 2,the sector plate .1 extends substantially diametrically Aover the endface .of the rotor. 'The angular distance between consecutive sealingstrips '9 is somewhat smaller than 'the sector angle of the plate '1.IConsequently, at any time, atleast one sealing strip'9 will slideon'the plate T on either sides ofthe axisof rotation so as to act as asealing member'between the air side vandthe gas side of thepreheater.Before a sealing strip comes out'of engagement with the platel, the nextfollowing sealing striphas already engaged thejplate. 'Betweenthetwosealing"strips,-the plate 1 and-the endfaceof the-rotor, 4there istemporarily -formed'a vclosedY space, and the air quantity enclosed insaid space Lis 4conveyed to the gas side. Similar conditions prevail atthe lower face of the rotor where closed spaces are formed between theplate 8 and the sealing strips I0.

In the operation of the air preheater, the pressure prevailing in theinlet part of the air duct may amount to, for instance, +3 inches ofwater, in the outlet portion of the air duct after the preheater to +1",in the gas duct before the preheater to -1.5", after the preheater to-4, in the space I3 between the rotor and the shell on the air side to-3/4 and in the corresponding space I4 on the gas side to 1.5". Onaccount of the pressure difference between the spaces I3 and I4, whichdifference according to the example amounts to .75" of water, part ofthe air will ilow over to the gas side along the periphery of the rotor.The leakage losses resulting therefrom can be entirely eliminated byreducing the pressure prevailing in the space I3 substantially to thepressure prevailing in the space I4 so as to stop the flow from the airside to the gas side.

To this end, the space I3 is by means of a conduit I5 connected to adraught fan I6 which maintains the pressure in the space I3 atsubstantially the same value as the pressure prevailing in the space I4on the gas side. As indicated in Figure 3, the air quantity withdrawnfrom the space I3 may be returned to the inlet portion of the air duct 3by a conduit I'I. However, it is deemed more suitable to discharge saidair quantity to the outlet portion of the air duct, as indicated inFigure 1. In order to avoid a decrease in temperature of the main airstream by the air quantity withdrawn by the fan, said air quantity maybe supplied, through a conduit i3, to a heat exchanger 20 provided inthe gas duct 5. 1n this heat exchanger, the air quantity withdrawn bythe fan can be heated to substantially the saine temperature as the mainair stream and is then united with the main air stream by means of aconduit 2I opening into the air discharge portion of the air duct.

As a result of the arrangements described, the volume flowing throughthe gas duct after the preheater is reduced by the quantity of air whichotherwise would leak from the space I3 to the space I4. The practicalimportance of this advantage will be evident from the fact that said airquantity may amount up to 15% of the total air quantity. Consequently,the power required for the ilue gas fan will be materially reduced, andthe devices for cleaning the nue gases can be made in a more simplemanner. The power required for the fan I6 is compensated for by acorresponding reduction of the power required for the fan for the mainair stream.

It may be suitable to provide additional sealing means between the rotorand the shell I2 along a plane at right angles to the plane of Fig. 1and through the axis of rotation I. For instance, such sealing means mayconsist of two sealing strips located on opposite sides of the axis ofrotation for separating the air side from the gas side and reducing thepower required for the fan I6.

As indicated by conduits 22 and 23 of Figure 1, the suction conduit I5of the fan may also be connected to the spaces between the sector plates'I, 8 and the cooperating sealing strips 9, I0 so as entirely or in partto eliminate the quantity conveyed through said spaces from the air sideto the gas side.

What I claim is:

1. An air preheater of the regenerative type comprising a rotor with anumber of axial passages therethrough provided with heat accumulati-ngelements and rotatable in a housing the interior of which has an airside and a hot gas side, said housing having axially aligned air inletand outlet ports at its air side and axially aligned hot gas inlet andoutlet ports at its hot gas side, and said rotor being rotatable aboutan axis intermediate and parallel to those of the air and hot gas portsof the housing to carry said elements successively through the hot gasand the air sides of the housing, said rotor having a side wallcooperating with the adjacent wall of the housing to dene acircumferential space around the rotor, said rotor at the ends of itspassages, being imperfectly sealed from said space so that air and hotgas from the rotor passages may enter said circumferential space at theair side and the hot gas side of the housing, respectively, at apressure diierential which promotes their intermingling, said preheaterbeing characterized by: a suction fan communicated with said space atthe air side of the housing for withdrawing air from the space at theair side of the housing at a rate such as to maintain the pressure ofthe air therein substantially equal to the pressure of the hot gases inthe space at the hot gas side of the housing, irrespective of the hotgas and air pressures which obtain in the rotor passages.

2. In an air preheater of the regenerative type comprising a rotor witha number of axial passages therethrough provided with heat accumulatingelements, and a housing in which the rotor is rotatable and the interiorof which has an air side at one side of the rotor axis, with air inletand outlet ports aligned on an axis parallel to that of the rotor, and ahot gas side at the opposite side of the rotor axis with hot gas inletand outlet ports aligned on an axis parallel to that of the rotor, saidrotor also having a circumferential wall cooperating with the housing todefine a circumferential space around the rotor whichvspace, at the hotgas and air sides of the housing, receives hot gas and air,respectively, from the rotor passages due to imperfect seals at the endsof the rotor passages, means for precluding intermingling of such hotgas and air in said space which results from the air therein having agreater pressure than that of the hot gas, said means comprising: asuction conduit connected to the housing in communication with the airside of said space; and a suction fan in said conduit for withdrawingair from said space at a rate such as to maintain the pressure of theair therein substantially equal to the pressure of the .hot gases in thehot gas side of Said space, irrespective of the hot gas and airpressures which obtain in the rotor passages.

3. The air preheater of claim 2, further characterized by an air outletduct communicated with said air outlet port; and further characterizedby duct means communicating said conduit with said air outlet duct forpassing the air withdrawn from said space into said air outlet duct.

4. The air preheater of claim 3, further characterized by a heatexchanger in said duct means for heating the air withdrawn from saidspace before the same is fed into said outlet duct.

5. The air preheater of claim 4, further characterized by a hot gasoutlet duct communicated with said hot gas outlet port; and furthercharacterized by the fact that said heat exchanger is located in saidhot gas outlet duct, so that air withdrawn from said space is passed inheat exchange relationship with hot gas which has emerged from the airpreheater, and is thereby preheated before being fed to said air outletduct.

6. The air preheater of claim 2, further characterized by an air inletduct communicated with said air inlet port; and further characterized byduct means communicating said conduit With said air inlet duct forconducting air withdrawn from said space back into said air inlet duct.

7. In a rotary air preheater of the regenerative type comprising a rotorwith a number of axial passages therethrough provided with heataccumulating elements, and a housing in which the rotor is rotatable andthe interior of which has an air side at one side of the rotor axis,With air inlet and outlet ports aligned on an axis parallel to that ofthe rotor, and a hot gas side at the opposite side of the rotor axiswith hot gas inlet and outlet ports aligned on an axis parallel to thatof the rotor, said rotor also having a circumferential Wall cooperatingwith the housing to dene a circumferential .space around the rotor, andsaid housing having sector-like end plates extending substantiallydiametrically across the end faces of the rotor, defining anintermediate zone in the housing and cooperable with radially extendingsealing members on the end faces of the rotor to temporarily form closedcompartments in the rotor as each rotor passage is carried through saidintermediate zone during rotor rotation and in which compartments air iscarried from the air side of the housing to the hot gas side thereof;means for t precluding intermingling of hot gas and air whichrespectively occupy the hot gas and air sides of said circumferentialspace around the rotor and which are received into said space from therotor passages due to imperfect seals at the ends of the rotor, saidmeans comprising a suction conduit connected with the housing andcommunicated with the air side of said space, and a suction fan in saidconduit for Withdrawing air from the air side of said space at a ratesuch as to maintain the pressure of the air therein substantially equalto the pressure of the hot gases in the hot gas side of said space; andmeans for substantially preventing air in said compartments carried fromthe hot gas side of the housing through the intermediate zone from beingtransferred to the hot gas outlet port of said housing, said meanscomprising a second suction conduit connected with one of saidsector-like end plates and communicated with said intermediate zone inthe housing and with said rst named suction conduit, at the suction sideof said fan, for withdrawing air from each of said closed compartmentsas the compartment moves through said intermediate zone during rotorrotation.

UNO OLOF BLOMQUIST.

References Cited in the le 0f this patent UNITED STATES PATENTS NumberName Date 2,229,691 Boestad Jan. 28, 1941 2,468,826 Karlsson et al. May3, 1949 2,471,995 Yerrick et al May 31, 1949 FOREIGN PATENTS NumberCountry Date 106,546 Australia May 25, 1927

